Electric motors are used for controlling or actuating specific components of an aircraft. For example, such motors are suitable for controlling the air buoyancy flaps of an airplane, but there are numerous further applications within an aircraft.
As possible types of motor synchronous reluctance machines are used, whose torque is generated on the basis of the reluctance force, for this purpose, the rotor cross-section is divided into so-called flux guiding and flux blocking portions, which are characterized by different magnetic resistances. The rotor itself generally is made of conductive sheet metal, in particular fabricated of a sheet package to avoid turbulent streams, wherein the lamination geometry of the individual laminations each is provided with flux guiding and flux blocking portions.
In the preferred magnetic direction (d-direction), a lower magnetic resistance occurs and the magnetic flux is guided well in the iron. In q-direction, the magnetic flux barriers impede the magnetic flux. Due to the overlap of rotor teeth and rotor barriers with stator teeth and grooves, a torque ripple occurs in such types of motor, when the rotor is rotated. This torque ripple can lead to undesired vibrations and to an increased noise emission, which is to be avoided in particular in applications of aircraft engineering.
A reduction of the torque ripple so far has been achieved by three known methods. On the one hand, it has been attempted to tackle the problem with the machine slope also known from other machine types such as asynchronous and synchronous machines. This procedure, however, requires an increased manufacturing expenditure, as the individual sheet packages of the machine portions must be positioned on the shaft very accurately. The angular offset between the individual portions determines the future torque ripple of the machine.
Alternatively, a combination of two different rotor geometries is taken into consideration. Here, two or more different barrier configurations of the rotor are combined on one shaft, in order to smooth the resulting torque by means of superposition of the barrier configurations. An example for the combination of different rotor cross-section geometries from different barrier configurations is given in FIG. 1. The geometries R-type and J-type were combined to a novel geometry. The resulting rotor has a total of four flux blocking portions with a barrier configuration, wherein the opposed barrier configurations are designed identical and the adjacent configurations are designed different.
Furthermore, there are rotor structures which by the position of the rotor tooth relative to the stator tooth reduce the ripple of the torque. The known geometries, however, are not constructed point-symmetrical with respect to the axis of rotation, which in motor operation can lead to imbalance and vibrations of the machine. To master these problems, individual laminations of the sheet package therefore must be rotated against each other on the shaft, in order to compensate the imbalance and vibrations. In this solution, however, it is disadvantageous that the resulting imbalance and vibration of the machine only can be compensated by an expensive rotation of the individual rotor sheets relative to each other. The angle of the rotation is to be determined by expensive methods, which renders the entire construction and the manufacturing method of the rotor very expensive.
This fact has a particularly disadvantageous effect on the use within an aircraft, as the motor vibrations can have a substantial influence on the flight safety of the aircraft and therefore should rather be avoided. However, the manufacturing method and the application of such synchronous reluctance machines within an aircraft also should be simplified.
The object of the present invention consists in indicating an aircraft with a synchronous reluctance machine, wherein the rotor is characterized by an optimized cross-sectional geometry which in an efficient way knows to avoid the torque ripple and the resulting vibration of the machine.
This object is solved by an aircraft with at least one synchronous reluctance machine comprising a stator with a plurality of grooves and teeth and a rotor with a plurality of magnetic flux barriers. Additional advantageous aspects of the aircraft are also described.
As compared to the known rotor cross-section geometries, the rotor according to the invention now is characterized in that at least one magnetic flux barrier is designed asymmetrical to the q-axis. The average of the magnetic reluctance hence constantly acts independent of the position of the rotor, so that the torque ripple is reduced. The motor hence can be operated in a stable way. In contrast to the prior art, the rotor however captivates by a simple structure of the lamination geometry and the composition on the rotor shaft. The production thereby is simplified and the manufacturing costs can be reduced systematically.
In rotor structures which consist of at least two segments, the ripple solely is reduced by their superposition, in case at least one flux barrier is formed asymmetrical.
In an aircraft, synchronous reluctance machines expediently are used for applications with a power class equal to or below 5 kW, as in such power classes the same are characterized by a particularly efficient mode of operation.
As a typical application profile of synchronous reluctance motors within an aircraft redundant drives, keyword “torque summing”, are conceivable, as in the case of possible motor faults of one side, in particular in the motor winding, no undesired consequences such as short circuits, drag torques, inductions, etc. will occur.
General key applications in principle are to be found in all electric actuators of an aircraft, in particular in electromechanical drives of the flight control, and in the landing gear actuation and steering system, or also for controlling a high-lift system of an aircraft.
It is preferred particularly, when due to the asymmetrical design at least one flux barrier is obtained independent of the rotor position, such that one flux barrier end of the at least one flux barrier substantially is opposed to a stator groove of the stator and the opposite end of the flux barrier substantially is opposed to a stator tooth. Particularly preferably, at least one end completely is opposed to a stator groove and the opposite end completely is opposed to a stator tooth. Mostly, however, the barrier end is located close to a groove or toothing.
In a preferred aspect of the invention, the stator includes a plurality of regularly spaced grooves and teeth.
An asymmetric design of the at least one flux barrier in particular is achieved in that the flux barrier angles of at least one magnetic flux barrier are chosen unequal. This means that for example one end of the magnetic flux barrier is inclined in direction of the q-axis and the opposite end is remote from the q-axis, i.e. inclined further in direction of the d-axis. Proceeding from a symmetric reference angle for both barrier ends, the angle on the one hand is increased and for the opposed barrier end the angle is reduced. The consequence is that independent of the rotor position the barrier ends each approximately oppose a stator tooth and on the other hand oppose a stator groove.
Ideally, the variation ranges of the flux barrier angles of at least one magnetic flux barrier are defined by the following equations:
                              Δθ          Stator                =                              360            ⁢            °                                N                          stator              ⁢                                                          ⁢              groove                                                          (        1        )                                          θ                      1            ,            max                          =                              θ            sym                    +                      Δθ            Stator                                              (        2        )                                          θ                      2            ,            min                          =                              θ            sym                    -                      Δθ            Stator                                              (        3        )                                          Δθ          Stator                ≥                              |                                          θ                1                            -                              θ                2                                      |                    2                                    (        4        )            wherein θ1,max/2,min represents the limit values for the unequal flux barrier angles, θsym represents the symmetric reference angle, preferably 135° for a 4-pole rotor, and ΔθStator represents the groove pitch of the stator.
From these equations it follows that the procedure for reducing the torque ripple according to the invention is independent of the pole pair number and the flux barrier number or the stator groove number of the reluctance machine of the aircraft.
An effective adaptation of the average reluctance of the rotor ideally is achieved in that at least the innermost magnetic flux barrier of a rotor gap is designed asymmetrical. Innermost flux barrier is understood to be that barrier which per magnetic flux blocking portion is closest to the rotor center and therefore has the largest opening angle. The end points of these barriers preferably with the one end point on the stator side cover or overlap a groove opening and with the other end point cover or overlap a stator tooth.
Ideally, all flux barriers of a rotor gap, i.e. of a flux blocking portion, are designed asymmetrical, wherein identical or unequal angles can be used for the different flux barriers. Expediently, all flux barriers of the rotor cross-section are asymmetrical. Ideally, the inner and outer flux barriers are parallel to each other, whereby the magnetic flux and the saturation behavior of the rotor can be kept almost constant.
In a particularly preferred aspect, the rotor cross-section is point-symmetrical to the axis of rotation, i.e. the flux blocking portions are point-symmetrical to the axis of rotation. Due to the point symmetry, the imbalance and vibration known from the prior art can be avoided a priori and a complicated arrangement or rotation of the sheets on the rotor shaft can be omitted in principle.
For the further reduction of the torque ripple it is expedient when the rotor is divided into one or more segments in axial direction, wherein a part of the rotor segments is mounted on the rotor shaft folded about the Z-axis, in particular folded about the Z-axis by 180°. Particularly preferably, the entire rotor construction consists of identically constructed laminations, wherein a part of the laminations is combined to various segments and the respective segments are arranged on the rotor shaft folded to each other by 180°.
By applying the sheet packages onto the rotor shaft, the resulting overall torque is superimposed, but the ripple of the torque is cancelled out by the phase shift. Due to the unequal and asymmetrical design of the at least one flux barrier, the mean torque however remains almost unchanged. Changes in the range of <5% are tolerable. Particularly preferably, the flux barrier angle is chosen such that a phase shift of the stator groove harmonic and possible of higher harmonics in the individual segments by about 180° is achieved.
Further advantages and properties of the invention will be explained in detail below with reference to an exemplary embodiment illustrated in the figures.